Evaporative cooling equipment such as cooling towers, evaporative condensers, and closed circuit fluid coolers are well known in the art. Such equipment has been used for many years to reject heat to the atmosphere. Cooling towers typically operate by distributing the water to be cooled over the top of a heat transfer surface and passing the water through the heat transfer surface while contacting the water with air. As a result of this contact, a portion of the water is evaporated into the air thereby cooling the remaining water.
In closed circuit fluid coolers and evaporative condensers, the fluid to be cooled, or the refrigerant to be condensed, is contained within a plurality of closed conduits. Cooling is accomplished by distributing cooling water over the outside of the conduits while at the same time contacting the cooling water with air.
In all applications of evaporative cooling equipment, proper water distribution within the equipment is critical to efficient performance of the equipment. Uneven distribution of water to the heat transfer surface will reduce the available air-to-water interfacial surface area which is necessary for heat transfer. Severe maldistribution of water may result in air flow being blocked through those areas of the heat transfer media which are flooded with water while at the same time causing air to bypass those areas of the media which are starved of water.
Generally, water distribution systems used in evaporative cooling equipment are either of the gravity feed type or the pressure spray distribution type. Gravity feed distribution system typically comprise a basin or pan which is positioned above the heat transfer media. In the bottom of the basin are positioned nozzles which operate to gravitationally pass water contained in the basin through the bottom of the basin while breaking up the water into smaller droplets and distributing the water droplets to the underlying heat transfer surface.
Pressure spray distribution systems, on the other hand, typically comprise multiple water distribution branches or headers, positioned above the heat transfer media with each branch containing a multitude of small spray nozzles. Generally, these nozzles are arranged closely in a uniform spacing in an attempt to achieve even water distribution across the typically rectangular top of the heat transfer surface.
Attempts have been made, especially in the utilization of pressure spray distribution systems, to develop nozzles which will allow for the reduction of the number of nozzles required in any given system while at the same time achieving uniform water distribution. However, in large towers nozzle clogging becomes a common problem due to the size of the tower components, allowing greater opportunity for foreign objects to find their way into the distribution system. To counteract this potential clogging problem, it is preferable on large towers to utilize nozzles with orifices as large as possible so that most debris can pass through the nozzle without becoming clogged. Unfortunately, as is known in the art, the larger the nozzle orifice, the more difficult it is to achieve uniform water distribution, so reducing the number of nozzles becomes an even greater challenge.
Another concern of cooling tower systems is the desire to keep the overall height of the evaporative cooling equipment to a minimum. This necessitates positioning the spray distribution system at a minimum distance above the top of the heat transfer surface. However, the closer the distribution system is to the top of the heat transfer surface, the less room there is for the water to be distributed evenly because of the smaller surface area the spray from each nozzle is generally able to cover.
Moreover, with any size of tower it is of critical importance to minimize the required spray water pumping pressure. Typically, pressure spray distribution systems have operated at spray pressures in the range of 3-8 psig (20.67-55.12 Pa). However, it is now desired to operate with spray pressures of no greater than 3 psig (20.67 Pa). This is especially true in very large towers since small increases in spray operating pressures can add hundreds of thousands of dollars to the operating cost of the unit over its lifetime. However, achieving uniform water distribution at low spray pressures is extremely difficult. This is due to the fact that at low spray pressures, there is very little energy available from the spray pressure to assist in spreading and distributing the water flow through the nozzles. It is also known in the art that the problems of low pressure distribution problems are further magnified by pressure losses occurring within the nozzle which are associated to the fluid frictionally scraping against the inside walls of the pipe. The magnitude of these frictional losses are influenced mainly by two factors which govern flow; flow turbulence and velocity profile shape. As explained in Chapter 6 of Handbook of Hydraulic Resistance, by I. E. Idelchik (Hemisphere Publishing Co., second edition, 1986), several other associated conditions or factors contribute to the magnitude of the turbulence and velocity profile factors, and they are: The Reynolds number; the relative roughness of the walls; the inlet conditions: relative length of straight starting section, the relative distance from the preceding shaped piece; and the geometric parameters of the pipe, like the angle of the bend, the relative radius of curvature, the aspect ratio, and the ratio of the inlet area to the exit area.
Each of these factors contribute to the magnitude of centrifugal forces which operate on the flow stream and hence, whether the presence of boundary layers along the walls of the pipe will appear within the velocity flow profile. As known, boundry conditions are adverse to uniform velocity flow profiles because they will cause a secondary flow within the pipe which is transverse to the actual fluid flow direction. This secondary flow is known in the art as the vortex pair, and the vortex formations impart enough centrifugal forces to the main flow stream to cause it to split into a dual pair spinning flow profiles that simultaneously travel down the pipe. The effect of of the dual flow profile, along with associated friction forces, causes the velocity profile of the flow stream to be non-uniform, namely, helically shaped.
In addition to vortex pair formation caused by the above-mentioned factors, the piping system itself will tend to create formations of separate vorticies or eddie currents. More specifically, the physically changing directions and angles of the pipework such as 90 degree bends or very sharp corners approaching that angle, will also cause an additional amount of pressure loss to be imparted to the flow stream. Under these specific conditions, flow will actually separate from the inner wall downstream of the 90 degree bend, intensifying pressure losses caused from vortex pair formations. The sum of these two types of pressure losses becomes even more pronounced when the flow velocity is increased.
It has been learned that in designing flow nozzles the pressure losses in the main flow stream from the above-mentioned friction factors have a direct relationship on the length and bore diameters of the nozzle. Typically, it has been found that the length to diameter ratio must be at least 1.5, and is preferably 2.0 or greater, in order to achieve acceptable flow distribution performance from the nozzle. Accordingly, it is imperative that with large cooling towers, these vortex pair formations be accounted for in the nozzle design, especially where water spray pressures are to be operated from 0.75 psig to 3 psig. However, accounting for pressure loss recovery by making the length to diameter ratio larger is a method which is undesirable since physical size and height limitations of a tower are a major cost concern.
To resolve the difficulties noted above, the present invention provides generally an improved fluid distributing nozzle which, when combined in a system comprising a plurality of such nozzles, provides even fluid distribution to an underlying surface over a wider range of operating pressures than prior nozzles without reduction in performance due to the frictional pressure losses within the nozzle.
The nozzle of the present invention is intended to operate at spray pressures in the range of 1-3 psig (6.89-20.67 Pa), though it has operated well at pressures as low as 0.75 psig (5.1675 Pa). The nozzle of the present invention is also considered large when compared to prior art nozzles, thereby minimizing the number of nozzles required in any given application. Accordingly, the nozzle of the present invention has been designed to maximize the operating characteristics of the nozzle through improvement of the flow profile entering the nozzle. By improving the entering flow profile, a more uniform velocity profile is maintained within the nozzle bore. This uniformity will help prevent formation of vorticies which can induce air into the nozzle and cause sputtering and vibration of the nozzle, ultimately reducing nozzle performance.
The nozzle of the present invention is related to the one disclosed in our pending application Ser. No. 738,681 filed Jul. 31, 1991 in which the main body has a substantially cylindrical bore therein. At about the midpoint of the main body, on its outer wall, is a pair of diametrically spaced supports for holding the nozzle in a header pipe. Four legs support a deflecting member in a vertically spaced relation under the cylindrical bore. The deflecting member is comprised of a top deflector which is in the shape of a four sided, acute angle pyramid and a bottom member which is in the shape of a frustum of a four sided obtuse angle pyramid. The top deflector is positioned on top of the bottom deflector such that the sides of the top and bottom deflector are generally aligned. This invention incorporates as an integral piece of the main body, anti-vortexing ears which are aligned in the same plane as the diametrically spaced supports.